(a) Field of the Invention
This invention relates to an improved process for esterification of 3,4-dihydroxyphenyl N-alkylaminoalkyl ketones with arylcarboxylic acid chlorides.
(b) Information Disclosure Statement
Minatoya et al. U.S. Pat. No. 4,138,581 Feb. 6, 1979) discloses amino-ketone compounds of the formula ##STR1## wherein Ar is phenyl or phenyl substituted by 1-3 members of the group consisting of alkyl having 1-4 carbon atoms, alkoxy having 1-4 carbon atoms, halo, trifluoromethyl, dialkylamino having 2-8 carbon atoms and alkanoylamino having 1-6 carbon atoms; R is alkyl having 1-4 carbon atoms or cycloalkyl having 3-6 carbon atoms; and R' is hydrogen or alkyl of 1-2 carbon atoms. Reduction of said compounds forms the corresponding phenylethanolamines useful as sympathomimetic agents. Said amino-ketones are in turn prepared by esterification of the corresponding diphenolic compounds of the formula ##STR2## with an acid chloride, Ar-COCl. The esterification is carried out either by reacting an alkali metal salt of the diphenol with the acid chloride, or by heating the hydrochloride salt of the diphenolic compound with the acid chloride in trifluoroacetic acid. Yields of the order of 30-50% are obtained.
The use of 4-dialkylaminopyridines and 4-(1-pyrrolidinyl)pyridine as acylation catalysts is known; cf. G. Hofle, W. Steglich and H. Vorbr u/ ggen, Angew. Chem. Int. Ed. Engl. 17, 569-583 (1978). The reference shows the substituted pyridines are effective as catalysts in acylation of both phenols and amines.